The primary goal of the satellites was to replace the U-2 spyplane in surveilling the Sino-Soviet Bloc, determining the disposition and speed of production of Soviet missiles and long-range bombers assess.

The KH-1 payload included the C (for Corona) single, vertical-looking, panoramic camera that scanned back and forth, exposing its film at a right angle to the line of flight.

[1]: 54 Launched 25 Jun 1959 22:47:45 GMT from Vandenberg LC 75-3-5 by a Thor-Agena rocket, the satellite was lost when its carrying Agena failed to reach orbit.

[1]: 54 As a result of the loss of Discoverers 3 and 4 during launch, the Air Force Ballistic Missile Division (BMD) halted flights until the Agena failures could be evaluated.

In consultation with Space Technology Laboratories, BMD slightly altered the Agena's propulsion, control, and computer systems.